Turning human waste into energy

A few weeks ago I lost the use of my toilet and learned firsthand just how much I missed it when it wasn’t there.

My plumbing went out of order when the pipe between my house and the city’s sewer line in the street collapsed. It was about 60 years old and made out of compressed fiberboard of some sort; I’m surprised it lasted as long as it did. Pipes like that belong to the homeowner, so it was my responsibility to get it fixed. It took about a week for the workmen to come and replace it with a plastic pipe. During that week I had to go to the local fast-food place to use the facilities. It got old fast.

More than 2 billion people around the world today don’t have a toilet or even an outhouse. They must relieve themselves beside the road, on the railroad tracks, or behind a bush. It’s a shocking and degrading picture to contemplate. I’ve been reading about sanitation — and the lack of it — in a book called “The Big Necessity” by Rose George.

Toilets and the modern treatment of human waste make a difference not just to our comfort, but to basic human health. Our bodily waste can carry bacteria, viruses, and parasites. If the waste comes into contact with water that’s later used for drinking, people can become violently ill.

In the early 1800s, some of the water companies in London took water from the Thames River for the use of their customers. Unfortunately, the water was contaminated with human excrement. A cholera epidemic in 1831 killed over 6,000 people and a bit later in 1848-1849 some 14,000 London residents died of cholera. In short, it really matters how human waste is cleaned up.

According to George’s book, the most complex or advanced toilets in the world today are Japanese. Some of them apparently have bidets (systems to wash your backside), heated seats, light switches you can hit when you visit the toilet at night, and control panels to run various functions of the commode. Our toilets are quite humble by comparison. But even our most simple ones get the basic job done: they take our waste away and launch it toward city sewage treatment plants or a septic tank in the backyard.

Perhaps it shouldn’t be a surprise that the Chinese work very hard to address their waste problem. With over a billion people, they have a monumental task in disposing of all that human waste on a daily basis. In the countryside one approach they sometimes use is a device called an anaerobic digester. It’s a vessel in which natural processes that break down waste without much oxygen present can proceed. Human waste is one material added to the digesters, but things like pig excrement can also be inputs. As they breakdown they form gas and solids that are less hazardous to human health.

One of the products of digesters is methane, called “biogas” in this context. It’s the same chemical that’s the main ingredient in the “natural gas” we burn in our furnaces. Biogas in some parts of rural China is used in the home as fuel for cook stoves. Compared to burning wood to cook, it’s convenient and of course it conserves trees.

Digesters can break down things other than sewage. The same basic biological processes can help break down agricultural waste. But the sewage-to-fuel process surprises people the most, an example of making something valuable out of hazardous materials.

On more than one occasion I’ve taken students to tour my local sewage treatment plant. (I realize I may be peculiar, but I think they should know what happens to their waste as part of being generally informed citizens and residents of the planet.) The anaerobic digesters at the plant produce methane. At least sometimes, that methane has been burned to provide heat to breakdown more waste. And sometimes it’s burned off in a flame atop the digester.

Most Americans don’t know much about where their waste goes or how it’s treated and released into the general environment. Here’s hoping we can get over our embarrassment about our bodily waste and educate ourselves at least about the basics of wastewater treatment.

Dr. E. Kirsten Peters, a native of the rural Northwest, was trained as a geologist at Princeton and Harvard. Her most recent book is “The Whole Story of Climate,” just published by Prometheus Books. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.

Thank you for this article, as a student of Sustainable Business, I’m keen on learning more about methods of converting waste into energy, specifically human waste and food waste.

As you rightly pointed out, anaerobic digestion is a clean source of energy, and at the same time, it takes care of waste disposal. Below as an interesting research, which in essence closes the loop, would love to hear your thoughts on it.